1. Field of the Invention
The present invention relates to a non-aqueous electrolyte secondary battery, and in particular to an anode electrode structure of a lithium ion secondary battery.
2. Description of the Prior Art
A lithium ion secondary battery or Li-ion rechargeable battery has many advantages compared with such conventional batteries as nickel-cadmium (Nixe2x80x94Cd) battery and nickel metal hydyride (Nixe2x80x94MH) battery.
Firstly, Li-ion battery as the non-aqueous electrolyte secondary battery has a high energy density so that it can work with 20 percent to 50 percent volume of conventional batteries of high-capacity Nixe2x80x94Cd and Nixe2x80x94MH despite being of approximately half a mass of those batteries.
Secondly, average voltage quantity of the Li-ion battery can generate a high voltage equivalent to approximately three times the voltage quantity of those of Nixe2x80x94Cd and Nixe2x80x94MH batteries.
Owing to above-described advantages, the Li-ion rechargeable battery has become a major and widely used battery type for mobile phones, handheld notebook computer, etc., as a power source.
Referring to FIG. 1, a conventional cylinder-shaped lithium ion secondary battery will be described. A conventional lithium ion secondary battery 1 comprises a cylinder-shaped container 2 housing a scrolled body or a jelly roll of a positive electrode body or an anode sheet 10 and a negative electrode body or cathode sheet 20. A pair of separator sheets 30 is disposed between the anode sheet 10 and the cathode sheet 20 such that the anode sheet 10 and the cathode sheet 20 are electrically insulated. An anode lead (not shown) of the anode sheet 10 disposed at the center of the jelly roll is electrically connected to the anode terminal 3 of the container 2 while a cathode lead 21 welded on the cathode sheet 20 is electrically connected to the negative terminal (not shown) of the container 2. As for the separator 30, a polyethylene micro-porous film is used. The scrolled body (hereinafter referred to as a jelly roll) is impregnated with an electrolyte of non-proton organic solvent in which LiPF6 is dissolved.
Referring to FIG. 2A, the anode sheet 10 is made of an aluminum foil coated with an anode active material layer 12. The aluminum foil is used as an electricity collection body and the active material layer 12 consists of compound metal oxide containing lithium. The active material is coated on front and rear surfaces of the aluminum foil. A blank space 111 is formed at one end of the anode sheet 10 to be welded with an anode lead 11. The anode lead 11 is electrically connected to the anode terminal 3 of the container 2 (see FIG. 1).
Now referring to FIG. 2B, the cathode sheet 20 is made of a copper foil coated with cathode active material 22. The copper foil is used as an electricity collection body. The cathode active material comprises a carbonaceous material capable of doping and undoping of lithium ions. The cathode active material layer 22 is formed on front and rear surfaces of the copper foil. At the end of the cathode sheet 20, a blank space 211 is formed for fixing a cathode lead 21 thereto. The cathode lead 21 is electrically connected to the cathode terminal of the container 2.
In such a jelly roll structure, a step of impregnating the electrolyte into the jelly roll is a time consuming process. This is because the jelly roll is minutely disposed inside the container and thus the electrolyte does not permeate into the jelly roll smoothly. For example, a step of causing an electrolyte impregnating process for a jelly roll having approximate length of 2 m and approximate width of 100 mm of anode and cathode sheets requires time not less than 10 hours.
As a method of solving such a problem, it is proposed to provide a plurality of electrolyte-guiding grooves on a surface of the cathode active material layer coated on a core foil as disclosed in the specification of Japanese Patent Laid-Open No. 9-293057. In this proposed structure, grooves are formed by applying pressure onto a surface of the cathode active material layer with a roller having a plurality of protrusions, so that the electrolyte can be easily introduced into a central region of the cathode active material.
However, by compressing the layer of the cathode active material for forming the electrolyte guiding grooves with a roller, the density of the active material layer is made uneven, which could worsen charge-discharge cycle characteristics as a non-aqueous electrolyte secondary battery.
Accordingly, an object of the present invention is to provide a non-aqueous electrolyte secondary battery that can reduce an injection time for impregnating an electrolyte into a jelly roll without causing the above mentioned uneven density of the active material layer. In a nonaqueous electrolyte secondary battery according to the present invention, a jelly roll comprises an anode sheet and a cathode sheet with a pair of separator sheets sandwiched therebetween. The anode sheet is coated with a plurality of regions of anode active material separated by a plurality of slit-shaped space regions elongating in a width direction of the anode sheet. The cathode sheet is coated with cathode active material.
The jelly roll is inserted into a battery can or a container having anode and cathode terminals which are electrically connected to the anode and cathode sheets, respectively. An organic non-aqueous electrolyte is injected into the jelly roll within the container such that the anode active material is impregnated with the electrolyte through the slit-shaped space regions.
Both ends of each of the slit-shaped space regions are extended to side edges of the anode sheet to enhance the impregnation process. These space regions are arranged in parallel to each other.
According to other aspect of the present invention, the plurality of regions of anode active material are further divided by an additional slit-shaped space region elongating in a longitudinal direction of the anode sheet so as to make a space network pattern by coupling the plurality of slit-shaped space regions to each other.
As for the space network pattern, other modification patterns may be used such that each of the slit-shaped space regions is disposed so as to intersect in a letter X, and is coupled to the above additional slit-shaped space region.
Each of the slit-shaped space regions may have such pattern that a central portion of each of the slit-shaped space regions is wider than those of end portion thereof.
Furthermore, each of the slit-shaped space regions may be disposed so that the adjacent distance becomes narrower toward the center of the jelly roll to equally enhance the impregnation process for entire region of the jelly roll.
Needless to say, the plurality regions of anode active material are formed on both surfaces of the anode sheet with the slit-shaped space regions.
It is preferable to set the total area occupied by the slit-shaped space regions to be less than 2 percent and not less than 0.5 percent of a total area of the anode active material.
It is also preferable to set the width of each of the slit-shaped space regions to be within a range of approximately 0.1 percent to 1.5 percent of width of the anode sheet.